You see your water meter bill, stare at the figure and curse those torrential downpours last winter that washed thousands of litres of water down the drain. All whilst you pay for the privilege of watering your garden with miles travelled treated drinking water. Seems backwards? It is.
Rainwater harvesting at home isn’t rocket science. It’s just collecting what lands on your roof and putting it to good use instead of letting it go into your sewers.
Over the years I’ve progressed from one basic water butt costing less than £40, to a system that collects enough rainwater to provide the majority of irrigation I need through the growing season. In this article I’ll guide you through how you can do the same.
Lets get an understanding of what harvesting rainwater actually entails, then talk about what you need to get started collecting rainwater, and how much it’ll cost you.
## Collecting Rainwater – The Basics
**Your Roof Is A Giant Cylinder**: Your roof collects rainwater. A 50sq metre roof on the average UK terraced house will yield roughly 30 litres of water for every millimetre of rain. It doesn’t sound like a lot but in the UK we average around 2mm of rain per rainfall event (here’s the data). So you’re getting about 60 litres of water per rainfall incident right off your roof. Over the course of a year your average UK roof collects thousands of litres.
Different materials will give you different percentages. Tile and slate roofs will collect as much as 90-95% of rainfall. Flat roofs are ok too provided they drain properly, however the collection rate here is a little lower at around 85%. It’s really downpipe positioning that matters though. If your gutters channel water run off to multiple downpipes around your home then you’ll lose more than if you can connect your water butts to a single downpipe.
**Water Quality**: Rainwater is naturally soft water so you’re getting all those benefits plants love about soft water. It’s going to be naturally slightly acidic at pH6.5 but nothing plants can’t handle. Compare that to mains water which is usually around pH7-7.5 and contains chlorine most plants are susceptible too, fluoride that plants don’t need and can’t use.
Leaves and bird poo washing off your roof will be a concern for some, but remember this water will be going on the garden and gardens can handle a little poo and decaying leaves in their water. First flush diverters built into most rainwater harvesting systems divert the first bit of runoff away from your storage. This washes most debris away.
**How Much Water Can You Save? ** The average uk household uses around 150 litres of water per day. Lets just say 30% of that is toilets, washing machines and watering the garden.
Rainwater can replace every single one of those uses. It’s easiest to start with the garden as you won’t need any special plumbing. Over the summer months if you’re watering every day those can add up to 50-100 litres per day depending on the size of your garden and how much you water.
That water you’ve just collected and isn’t coming from your meter will save you money on your water bill. A cubic metre of water (UK households are billed per cubic metre) is 1000 litres. With water prices working out at an average of £1.50 per cubic metre including sewerage charges.
Yeah thats’ not going to change the world. But let me throw some numbers at you. A small set up that collects 10,000 litres per year would save you £15 per year. A medium that collects 30,000 litres would save you £45.
At current water rates those set ups pay for themselves in two to five years. Then start saving you money for the rest of their life time.
## Rainwater Collection Kits & Components
I’m going to break down the basic components of domestic rainwater harvesting that you’ll need, plus useful accessories and how much they’ll cost.
### Water Butts
Water Butts are the storage vessels that collect your roof rainwater runoff. Most start at around £19.99 for a basic model (Water Butts Direct), however if you’re going to bother collecting rainwater you’ll want a bigger capacity than that.
A good size to aim for is 200 litres. This particular water butt (Rainwater Direct) is just over 57cm across and 97cm tall. Big enough to store plenty of water without sticking out like a sore thumb in your garden.
If you’re watering a reasonable sized garden 200 litres will give you weeks worth of stored rainwater for normal watering jobs. By reasonable I mean a moderate sized domestic garden that you aren’t watering every day.
Want to irrigate larger areas or cut down on mains water usage even further? You’ll either need to link a few butts together or spend money on a larger capacity container. Make sure you’re storage matches your roof run off potential and your typical water usage.
### Rainwater Diverters
This is where it all falls down for some people. Or literally in the case of bad rainwater diverters. What you’ll need to do is fit a downpipe rain diverter to connect your guttering to your storage container.
Rain diverter products start from £14.50 and go up to £26.00 inc VAT(Celtic Water) depending on the model you go for. They’ll all basically do the same job, which is connect to a standard downpipe and divert water into the tank whilst allowing rainfall to continue down the downpipe as normal when the water butt is full.
The downpipe rain diverters shown above fit standard 68mm round plastic downpipes and 65mm square plastic downpipes (Save Water Save Money). These are the standard dimensions used on most uk housing so should work for pretty much everyone.
Once full, the excess water simply continues down your original drain. Which means you don’t have water overflowing around your foundations or causing damage to paths and courtyards.
### Connecting Parts
Couplers and connectors to link your diverter to your water butt storage container. Most shop bought kits will include these however if your building a system from separate parts make sure you have connectors that allow you to hook up your downpipe diverter to your tank.
Couplers need to be waterproof and able to cope with high volumes of water moving through them quickly. Again these are included in most complete rainwater harvesting kits these days so you shouldn’t have to think about it too much (The Rain Harvesting Store).
A 3P downpipe filter collector and tank connector kit is advertised as being easy to fit yourself which leads me to believe these systems are all designed with the DIY market in mind. They come complete with a filter which keeps debris out of your water butt.
### Additional Kit Components
Ok so that about covers it for basic set ups. But if your feeling fancy you can add taps, valves, better quality lids or even pumps to pressurise your rainwater collection for irrigation systems and inside usage.
Remember though this is a guide to cheapest rainwater harvesting kit. You won’t need any of these extras for garden watering.
## Prices of Complete Kits
So lets talk money…
### The Basic Rainwater Harvesting Kit
At it’s simplest and cheapest a complete 200 litre water butt kit complete with everything you need to harvest rainwater is available for £29.99 (Save Water Save Money). That includes a diverter that is 20 inches long (Save Water Save Money).
This is the cheapest its possible to get away with and still have a functioning rainwater collection system that actually collects rainwater. If you don’t own some of the tools mentioned in the previous section you’ll need to add another £10-15 onto that for basic tool kit.
Total cost is now sitting at under £45 for a rainwater harvesting system that you can build in a day over a weekend.
Theres good news and bad news about starting at this level. The bad news is that for some properties it won’t make much difference to your water usage.
I say that because your roof is collecting rainwater at a rate of 30 litres for every millimetre of rainfall. So a light shower will fill up a small water butt very quickly. Then you’ll be back to using water from the mains for watering your garden.
The good news is it will show you whether rainwater harvesting works for your property and how much water you can actually save. Theres alot of scope to expand later on as I will cover down below.
This can easily handle the majority of my watering requirements during the growing season. You’d be mad not to at least start here and see how you get on.
### Mid Range
One of these (Checkatrade) will set you back as little as £70. Providing your willing to spend that little bit extra on a better quality water butt, more storage and maybe even multiple water butt setups.
Now we’re starting to talk about systems that can handle a reasonable size garden with ease. As well as some grey water usage inside the property.
Connecting rainwater direct to toilets and washing machines is possible, but requires alot more work than is needed for garden irrigation and watering pots on the patio. You can get fully plumbed systems that connect direct indoors however these kits price themselves well into the hundreds.
### Advanced
This DIY utopia (Checkatrade) will set you back £750. That my friends is now taking rainwater harvesting properly grounded in the realm of “maybe you should call a plumber”.
Not that there’s anything wrong with that. If your feeling adventurous and have some DIY experience you could still probably tackle a project of this size. However we are fully expecting a proper professional to come install it now.
Lets take stock shall we?
Systems this big incorporate pumps to pressurise the rainwater. Better filtration systems, more storage capacity and the necessary plumbing to connect directly to your households indoor plumbing.
When it comes to spending your hard earned money on a rainwater harvesting system remember this. The more you spend, the more water you can harvest from rainfall, the less you’ll be spending on your water bill from your meter.
Mistake #1: Don’t expect it to do your whole garden.
A common complaint I hear is that rainwater harvesting won’t provide enough water. The trick is to size your system to match your roof run off potential. A medium sized rainwater harvesting system should provide all the water you need for garden irrigation providing you have a typical roof size.
No system is going to completely replace mains water for watering your garden. That would require a butt for every square metre of roof!
Larger systems can cover toilet flushing and watering lawns, but remember rainwater should always be used on the garden first. So always allocate some of your rainwater to the garden unless your water butt is properly massive.
Mistake #2: Think your downpipe is standard.
Measure your downpipes before ordering. Mainly because its a pain to get your hands on that kit if you realise your downpipe isn’t 68mm round or 65mm square after you’ve bought it.
You’ll notice I mentioned above that rainwater diverters fit standard downpipes. Yeah well my house has a mix of round and square plastic downpipes (Save Water Save Money) and guttering as its older.
So when I bought my first rainwater diverter off amazon I ended up with this:
…that didnt fit. Dont be like me. Check first.
Mistake #3: Position butts awkwardly
Water butts ideally need to be located where they can empty directly into them. So near downpipes is a must unless you plan to run extensive plumbing.
They also need the overflow run off area to be cleared so that when the butt is full water has somewhere to go. Positioning your butt up against the house and pointing the overflow spout directly at the foundations isn’t ideal.
Likewise if you live somewhere that gets freezing winters and place your water butt where it will freeze solid every winter you’re asking for problems.
D
Mistake #4: Over estimate savings
Rainwater collection systems don’t cancel your water bill. A good sized basic rainwater harvesting system will noticeably reduce your water bill. During summer months when you use more water for garden irrigation you’ll see it more.
## Installing Your Rainwater Harvesting System
So far so information overload. Lets put some feet to the ground…
Firstly. You need to check your property. Walk around when it rains and see how water runs off your roof. Identify where guttering dumps water into downpipes and how much water each downpipe deals with.
You’ll quickly see which downpipes are better placed to connect a water butt too. Also take a look where overflow will drain away to when butts are full. This is where you’ll position your water butts.
Now you know roughly where you want your system located, check the ground is level and can support the weight of a full water butt. Two hundred litres of water weighs 200kg and thats not including the weight of the water butt itself.
If your ground is too soft butts can sink as they empty and fill. Positioning your butt on a concrete block or paving slab will usually rule out any problems.
Positioning also matters when we get onto the topic of use. If your system is difficult to get too for cleaning and extraction taps wont be used. Thats counter intuitive to having a rainwater harvesting system in the first place.
Position butts where its convenient to use and clean.
### Your Downpipe
Once you know which downpipe you’re going to use you need to cut into it to install your rainwater diverter. Dont worry it sounds worse than it is, but there are a few things you need to know.
Cut your downpipe about 30cm up from ground level. You want to allow enough space to attach the rainwater diverter without the butt being so high you cant use it.
Use a proper pipe cutter not a hacksaw. You’ll get cleaner results and less hassle. When fitting your rainwater divert check the drain holes on the butt are covered by the absorber tray that connects the two.
Test fit your diverter and make sure it stays put when its full of water. Most diverters come with rubber seals to ensure a watertight connection between downpipe and water butt connector.
Once your happy test it with a hose pipe. Make sure theres no leaks and that excess water continues to drain away from your property when the water butt is full.
Connect your down pipe diverter to your water butt using the included connector kit. You’ll probably run a short length of hose pipe from the outlet on the diverter to a connector on the butt.
Place connector high enough on the butt to allow good flow rates, but low enough that most of the water butt can be used.
Once you’re happy cut away the excess pipe leaving a clean finished edge. You know the drill by now. Check all seals and connections. Make sure your butt has a tap near the bottom that’s easy to get your watering can under.
If your planning on using your rainwater for irrigation systems you’ll also need a suitable hose connector.
## Rainwater Harvesting Maintenance
Once everything’s installed and you’ve used your rainwater butt for a few seasons you’ll need to perform some maintenance to keep everything running smoothly.
Clean debris from gutters and downpipes atleast twice a year. Winter when leaves have fallen and spring before the heavy spring rainfall.
Blocked gutters = less water in your butt. If guttering cant handle the run off when butts are full they’ll overflow onto the ground. Which kind of defeats the object.
Empty and clean your rainwater diverters downpipe connector seasonal. Leaves moss and God knows what else collects in there and can prevent it operating correctly.
Keep an eye on your butt for any signs of cracks or wear. Sunlight will degrade most plastics over time. You don’t want your water butt bursting as you fill it.
In winter there’s always the danger of water freezing inside tanks and cracking the plastic. Or freezing as it pours from the downpipe causing obvious problems.
Thats why some water butts come with drain points allowing you to easily drain them down over winter. If your not wanting to chance it, or live somewhere that doesn’t get freezing winters wrap em up!
Cover your rainwater butt to prevent Algae growth. Sunlight causes algae to grow, which although not harmful to health; looks pretty rubbish.
Also use a butt with a lid. Allows you to stop leaves and debris blowing into your water butt. No more dodgy green gloopy water.
Rainwater harvesting systems should be emptied and cleaned once a year. It’s a pain but will prevent most headaches caused by algae or debris built up over time.
### Rainwater Harvesting FAQs
How do you set up a rainwater harvesting system?
Installing a rainwater harvesting system really is just common sense. Identify where water is draining to on your property, where you can position water butts and connect them to downpipes. Measure downpipe sizes, order parts and have fun.
How much does a rainwater collection system cost?
At its cheapest you can pick up a basic kit that allows you to harvest rainwater from your roof for around £30. Complete plumber install systems that work with indoor plumbing start at £750 and can cost thousands.
What’s the smallest rainwater tank you can get?
As small as two hundred litres. Although these are designed for external use only so you’ll have to move watering cans about to use it. Think irrigation systems or villas with interior courtyards.
Can I put a water butt against my house?
You can however if your property floods when it rains you wont have issues when the water butt overflows! Also dont position your butt where it will freeze solid in the winter and crack itself up.
Will rainwater harvesting save me money?
Probably not millions but having a correctly sized system for your property will dramatically reduce your domestic water usage therefore saving you money each year. Unless water becomes completely free..? Hmm.
How much money can I save with rainwater harvesting?
Ignore those companies telling you you can save £300 a year. Even if every single drop of rainwater was used on your garden you’d struggle to save more than £100 a year. The maths dont lie.
How much water can you save with rainwater harvesting?
It all depends on the size of your system and roof run off potential. A medium rainwater harvesting system that replaces irrigation water on a medium sized garden would easily save 10,000 litres per year. That’s £15 saved on your water bill.
How many rain barrels do I need?
Just one will be enough! You’ll soon find out pretty quick wether you have enough storage or not. If your still watering with mains water regularly get another butt.
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